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A – Operating Theory
DPN 402197 © TSS (International) Ltd Page 3 of 10
A.3 SIGNAL ISOLATION
Marine survey environments suffer from significant levels of background noise pro-
duced by other electrical systems on board the ROV. The 350 System must remove
this noise from the coil signals before it can perform meaningful calculations.
This noise reduction process involves many stages, including:
1. BAND-PASS FILTERING:
Signals received by the coils may be extremely weak – possibly less than 5µV in
amplitude. Each of the six windings in the coil array therefore includes a precision
pre-amplifier and filter board to apply amplification and signal conditioning before it
transmits the signals to the relatively noisy environment on board the ROV. The pre-
amplifier can vary its overall gain automatically according to circumstances.
An additional function of the pre-amplifier board is to apply high-pass and low-pass fil-
tering. This function limits the pass-band of signals that arrive at the SEP to between
7.2Hz and 300Hz.
2. Frequency spectrum analysis
The SEP converts the analogue signals supplied by the coils to an 18-bit digital for-
mat for processing by the digital signal processor (DSP). Figure A–2 shows a simpli-
fied block diagram of the signal path for three of the six channels in the 350 System.
Figure A–2: Simplified signal path
The SEP samples the supplied signals approximately 1000 times per second and
uses powerful signal processing techniques to determine the spectrum of received
frequencies.
After processing the signals in this way, the SEP divides the entire received spectrum
into narrow ‘windows’ as shown in Figure A–3. The System stores the instantaneous
signal amplitude for each of these ‘windows’ in a series of memory locations.
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